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Deciphering Heat Emergencies
By Dr. Ken Lavelle, MD, NREMT-P
It is the middle of July and the northern states have been experiencing a heat wave. Of course this is the perfect time for a stubborn structure fire. It has gone to the third alarm for manpower as the temperatures are in the 90s with 80 percent humidity. As crews cycle through rehab you know you need to watch for heat emergencies, but what exactly do you need to look for?
It is helpful to first discuss how body heat is generated, and how it is dissipated.
Our bodies constantly generate heat. This maintains our ideal body temperature. It is also a byproduct of our normal metabolism. The amount of heat generated increases with an increase in physical activity.
Heat is dissipated in four ways: convection, conduction, radiation and evaporation. Convection is dissipation of heat when a fluid passes over the skin — typically air, but it can be water as well if the person is submerged. Conduction is loss through direct contact with a cooler substance, such as lying on the cold ground in the winter. Radiation is the release of heat into the environment. Evaporation is the loss of heat that occurs when moisture on our skin goes into the air.
Firefighters in full gear are at high risk for heat emergencies because they are generating more heat and have limited the ability to lose the heat. Bunker gear limits virtually all of the methods of heat dissipation to some degree. In addition, evaporation is decreased when the ambient humidity is high. With this in mind, lets look at the potential heat emergencies we may encounter.
Heat emergencies come in a spectrum — a range from relatively minor to more serious and life threatening. It is important for the EMS provider and others to be able to rapidly identify who is at risk for serious illness and even death and be able to manage these patients effectively. This month we will look at this spectrum of diseases with an emphasis on being able to differentiate between them.
Cramps during activity in warm weather are common. They usually occur after several hours of activity, and can even occur during cool down in rehab or after the fire. They are often caused by electrolyte imbalances due to rehydration with water only and not a salt-containing fluid. Any large muscle group can be involved, including the back or the abdomen, but the lower extremities are more commonly involved. The body temperature can be normal or slightly elevated, and there are usually no other serious systemic signs or symptoms.
Treatment consists of rehydration with an electrolyte-containing fluid such as a sports drink. In rare cases, an IV may be necessary if the cramps are severe and not improving with oral fluids. Transport to the hospital is usually not necessary.
Heat exhaustion is the next stage and involves minor complaints related to dehydration and mildly elevated temperature. Symptoms include thirst, dizziness, headache and general malaise. Mental status is generally intact and there are no major neurological issues such as seizures. The victim may have nausea and vomiting, which can complicate treatment.
Treatment involves removing the victim from the heat source, a good physical assessment, monitoring vital signs, and rehydration. If the patient has no nausea symptoms, rehydration may be able to be accomplished orally. Otherwise an IV may be necessary. If an IV is placed, and possibly for other patients as well, consider checking the blood glucose level. Low glucose may cause some of the complaints as well. Gentle cooling can be initiated, such as with a wet towel around the neck or with misting fans. Reevaluate after a period of time, such as 30 minutes — if the symptoms have been resolved, then hospitalization may not be necessary.
Heat stroke is the life threatening condition that we cannot miss. The primary difference between heat stroke and heat exhaustion is the mental status and neurological status. A heat stroke victim has the symptoms of heat exhaustion, but also has a change in mental status — loss of consciousness, confusion, combativeness or simply just “not all there.” Sometimes this can be subtle. They also may have seizures.
This is one of the main reasons that when a firefighter comes into the rehab sector I just try to chat with them a bit. I’ll ask how they are feeling and if they have any complaints, but also about the fire or scene — what did they find inside or any other information about the response. I can use this information to help determine if they are oriented or confused. If still unsure, ask a buddy that knows them if they are acting normally. Friends or co-workers will be able to pick up on subtle changes that we may not be able to notice because we do not know them as well.
There are 2 types of heat stroke — classical and exertional.
Classical Heat Stroke is related to environmental exposure and often affects the elderly and those with significant medical history. It may develop slowly, over days, and include a minimally elevated body temperature.
Exertional Heat Stroke affects young, healthy individuals. Its onset is rapid and the temperature of the victim is often very high. The individual is simply generating heat faster than the body can dissipate it. This is the type of heat stroke that would be more likely to affect firefighters.
Although many rehab sectors will check for temperature, it really isn’t necessary. There are other symptoms that are used to determine this differential diagnosis. In addition, oral, tympanic and cutaneous temperatures are not reliable. The only reliable gauge of core body temperature is the rectal temperature, and in the hospital this will be initiated for suspected heat stroke victims. I think we can agree that this would not be practical on the fireground.
Treatment here involves a good assessment, vital signs, oxygen and rapid cooling. The victim needs to be stripped to their undergarments. Ice packs can be placed in the groin and armpits — areas where large blood vessels are close to the skin. The most effective method of cooling is spraying the body with a tepid mist and having fans conduct air across the body. Cooling is often halted at approximately 100 degrees Fahrenheit to avoid over cooling. Rapid transport to the hospital with ALS in attendance is indicated. Mortality can reach 10 percent.
As always, follow local protocol. If there are numerous EMS resources and advanced providers present, care may be able to progress on scene for the minor cases. In the absence of these resources, earlier transport may be required. The key is to be able to identify heat stroke and initiate immediate treatment. We can help with prevention as well by encouraging the proper type and amount of fluids. It is much easier to prevent heat emergencies than treat them.